Pistons for internal combustion engines or for compressors

ABSTRACT

A light metal piston, for an internal combustion engine or a compressor, has a crown with a skirt integrally connected to the crown around the opposing thrust faces of the piston and providing a closed internal cavity with the crown. An insert of lower coefficient of expansion than the light metal, conforming to the internal shape of the skirt, is superimposed on the inner surface of the skirt. The insert is formed as two independent parallel bands extending from a gudgeon pin boss, the bands being joined by a connecting portion. One of the bands is an upper band positioned nearer the crown while the other band is a lower one positioned nearer to the open end of the skirt with the upper band exerting much less control than the lower band.

United States Patent 1191 Cockcroft 1451 Sept. 30, 1975 PISTONS FOR INTERNAL COMBUSTION ENGINES OR FOR COMPRESSORS [75] Inventor: Frederick Edward Cockcro'ft,

Allerton, England Filed: Feb. 21, 1974 Appl. No.: 444,477

Related US. Application Data [63] Continuation-in-part of Serl No. 276.468. July 31.

1972. abandoned.

FOREIGN PATENTS OR APPLICATIONS 287.154 12/1928 United Kingdom 92/228 466,739 6/1937 United Kingdom... 92/230 701.291 12/1953 United Kingdonr. 92/230 311.123 9/1933 Italy 92/228 Primary l; .\'uminerlrwin C. Cohen Almrney. Agent, or FirmEdward F. Connors 57 ABSTRACT A light metal piston, for an internal combustion engine or a compressor, has a crown with a skirt integrally connected to the crown around the opposing thrust faces of the piston and providing a closed internal cavity with the crown. An insert of lower coefficient of expansion than the light metal, conforming to the internal shape of the skirt, is superimposed on the inner surface of the skirt. The insert is formed as two independent parallel bands extending from a gudgeon pin boss, the bands being joined by a connecting portion. One of the bands is an upper band positioned nearer the crown while the other band is a lower one positioned nearer to the open end of the skirt with the upper band exerting much less control than the lower band.

7 Claims, 6 Drawing Figures US. Patent Sept. 30,1975 Sheet20f3 3,908,521

US. Patent Sept. 30,1975 Sheet 3 of3 3,908,521

PISTONS FOR INTERNAL COMBUSTION ENGINES OR FOR COMPRESSORS This application is a continuation-in-part application of application Ser. No. 276,468, filed July 31, 1972 and now abandoned.

This invention relates to a light metal'pistons for internal combustion engines or compressors. That is, pistons made of aluminum, magnesium or similar metals and their alloys.

According to one aspect of the invention, a light metal piston for an internal combustion engine or a compressor has a crown, a skirt integrally formed with said crown around the opposing thrust faces of the piston in a manner to provide therewith a closed internal cavity, gudgeon pin bosses having bores opening into said cavity, and two expansion-control inserts made of a material of lower coefficient of thermal expansion than the light metal. Each insert has a pair of connecting portions each anchored in a gudgeon pin boss; a pair of first bands superimposed on the inner surface of the skirt and not embedded therein, each extending from a said connecting portion at least part-way round one of said thrust faces to form a bimetallic element therewith, each said first band being near the crown end of said skirt; a pair of second bands superimposed on the inner surface of the skirt and not embedded therein, each extending from a said connecting portion, being spaced apart from and substantially parallel with said first bands, each said second band extending at least part-way round one of said thrust faces to form a bimetallic element therewith, and each said second band being nearer to the open end of said skirt than each of said first band; and a pair of further portions each interconnecting one of said connecting portions, one of said first bands, and one of said second bands, with another of said connecting portions, first bands, and second bands. The second bands, being nearer to the open end of said skirt, exert a greater degree of thermal expansion control for a given temperature change than do said first bands which are near the crown end of the skirt. Each of said further portions may extend around a said gudgeon pin boss and interconnect a pair of said connecting portions each anchored in opposite sides of the same gudgeon pin boss. Also in this case, each expansion control insert may be symmetrical about a longitudinal plane of the piston substantially containing the axis of the gudgeon pin bores.

Alternatively each said further portion consists of an extension of one of said pairs of bands interconnecting the ends of the bands of a said pair, which ends are remote from said connecting portions, and said further portions pass right around the interior surface of the opposing thrust faces of the piston skirt. Inthis case, each expansion control insert is symmetrical about a longitudinal plane of the piston substantially at right angles to the axis of the gudgeon pin bores.

Three embodiments of the invention are described, by way of example only, with reference to the accompanying drawings, in which:

FIG. I is a section in a plane which is normal to the gudgeon pin axis but which includes the piston skirt axis,

FIG. 2 is a section along the line 2-2 of FIG. 1,

FIG. 3 is a section similar to FIG. 1 of another embodiment,

FIG. 4 is a section along the line I(K of FIG. 3,

FIG. 5 is a section similar to FIG. 1 of a further embodiment of the invention, and

FIG. 6 is a section along the line 66 of FIG. 5.

In the drawings, items performing the same function are accorded the same reference numerals.

Referring initially to FIGS. 1 and 2, a light metal piston has a crown 10, piston ring grooves 11, a skirt l2 and gudgeon pin bosses 13 in which are formed gudgeon pin bores 14. The gudgeon pin bosses 13 are formed on parallel chordal localized flats 15 on the sides of the piston positioned circumferentially between a thrust face 16 and a non-thrust face 17. The faces 16, 17 will be referred to in the specification as the opposing thrust faces, even though the thrust exerted on one face is very much greater than that exerted on the other, depending on the direction of rotation.

When the piston is raised to working temperature, expansion of the light metal skirt 12 is controlled by an insert made of a material of lower coefficient of thermal expansion than the light metal. A suitable material for the insert is sheet mild steel. The insert and the piston skirt thereby form a bimetallic element.

The insert in FIGS. 1 and 2 consists of upper bands l8 and lower bands 19. The upper and lower bands l8, 19 are parallely spaced apart by insert connecting portions 20 which abut against or are bonded into the gudgeon pin bosses 13. The two connecting portions 20 are joined together by a further portion 21 of the insert which passes around the gudgeon pin bore 14 on the opposite side from the piston crown 10. The bands l8, 19 are shaped to conform to the internal shape of the piston'skirt and conveniently terminate against abutments 22 cast on the inside of the piston skirt 12.

It will be seen that the axis 23 of the gudgeon pin bores 14 is parallely spaced from the plane containing I the axis 24 of the piston skirt 12. The gudgeonpin axis 23 is displaced towards the thrust face 16. In a piston of this construction the insert is preferably positioned symmetrically relative to the piston skirt 12 but not relative to the gudgeon pin axis 23.

FIGS. 3 and 4 show a piston generally similar to that shown in FIGS. 1 and 2. Furthermore, the two mild steel inserts again have upper and lower bands 18, 19 joined by connecting portions 20. However, in this case there is not further portion 21 passing around part of the gudgeon pin bore 14. Instead, the upper bands 18 do not stop at the abutments 22 but pass right round the interior surface of the piston from one gudgeon pin boss 13 to the other. If preferred the upper bands 18 can be stopped against the abutments 22 and the lower bands 19 can be made continuous. Alternatively both upper and lower bands 18, 19 can be made continuous and the abutments 22 omitted.

FIGS. 5 and 6 show a piston generally identical to that shown in FIGS. 1 and 2 except that in FIGS. 5 and 6 the further portion 21 of the insert passes between the gudgeon pin bore 14 and the piston crown 10.

It will be noted from the above description that in the present invention the piston crown is integrally connected to the upper ends of the opposing'thrust faces of the skirt, there being no transverse slot and the skirt and crown forming a closed internal cavity in the piston, and the ferrous insert is formed in two distinct, independent, expansion-controlling bands (the upper band 18 and the lower band 19) both of the same thickness. It will be cleat that, because of the influence of the crown, the upper band 18 will exert very much less control than the lower band 19 which cooperates with a relatively thin portion of aluminum skirt. The flexibility of the skirt itself allows the lower bands to exert a much greater degree of influence on the skirt shape and, in particular, on the expansion parallel to an axis at right angles to the axis of the gudgeon pin bores.

It should be especially noted that the two bands l8, l9 are entirely separate and independent from one an other, except in the regions of connecting portions 20, which are anchored in the gudgeon pin boss. And the bands are superimposed on the innersurface of the skirt and not embedded therein.

This important feature of allowing the lower ferrous band 19 to have greater influence over skirt expansion than the upper band 18 is nevertheless achieved by the use of only two ferrous inserts per piston, thus avoiding manufacturing difficulties which would result from the use of four or more inserts per piston. In the embodiments of FIGS. 1 and 2 and FIGS. 5 and 6 the two inserts are symmetrical about plane 24, whereas in the embodiment of FIGS. 3 and 4 the inserts are symmetrical about an axis at right angles to the axis of the gudgeon pin bores.

The construction of each of the embodiments has two major advantages:

1. It gives a greater degree of thermal control of the lower end of the piston skirt than of the crown end for a given temperature change, without the necessity of upper and lower ferrous inserts of metals having different coefficients of thermal expansion, and

'2. lt allows, through the absence of transverse slots on the opposing thrust faces, stresses to be transmitted directly between the crown and skirt on these faces.

What is claimed is:

l. A light metal piston for an internal combustion engine or a compressor having a crown, a skirt integrally and completely connected to said crown around the opposing thrust faces of the piston in a manner to provide 'a closed internal cavity in the piston, gudgeon pin bosses having bores opening into said cavity, and two expansion-control inserts made of a material of lower coefficient of thermal expansionthan the light metal, with each being superimposed on the inner surface of the skirt each said insert having a pair of connecting portions each anchored in a gudgeon pin boss;

a pair of elongated first bands, having the inner face thereof entirely open to said cavity each extending from a said connecting portion at least part-way round one of said thrust faces to form a bimetallic element therewith, each said first band being near the crown end of said skirt; pair of. elongated second bands, having the inner face thereof entirely open to said cavity each extending from a said connecting portion, being spaced apart from and substantially parallel with and independent from said first bands, each said second band extending at least part-way round one of said thrust faces to form a bimetallic element therewith, and each said second band being nearer to the open end of said skirt than each of said first band; i and a pair of further portions each interconnecting one of said connecting portions, one of said first bands, and one of said second bands, with another of said connecting portions, first bands, and second bands,

whereby said second bands, being nearer to the open end of said skirt, exert a greater degree of thermal expansion control for a given temperature change than do said first bands which are end of the skirt.

2. A light metal piston as claimed in claim '1' whereineach said further portion extends around a said gu d-' geon pin bore, and interconnects a pair of said connecting portions each anchored in opposite sides of the same gudgeon pin boss. 7

3. A light metal piston as claimed in claim 2 wherein each expansion control insert is symmetrical abouta longitudinal plane of the piston parallel to afnd adjacent to the plane containing the axis' of'the 'gudgeon pin bores. I

4. A light metal piston as claimed in claim 1 wherein each said further 'portion'consists of an extension of one of said pairs of bands, interconnecting the ends of the bands of said pair, which ends are remote fror'nsaid connecting portions, and said further portions passing said further portion extends below the gudgeon pin bore.

7.'A light metal piston as claimed in claim '2 wherein" said further portion extends above the gudgeon pin bore.

near the crown 

1. A light metal piston for an internal combustion engine or a compressor having a crown, a skirt integrally and completely connected to said crown around the opposing thrust faces of the piston in a manner to provide a closed internal cavity in the piston, gudgeon pin bosses having bores opening into said cavity, and two expansion-control inserts made of a material of lower coefficient of thermal expansion than the light metal, with each being superimposed on the inner surface of the skirt each said insert having a pair of connecting portions each anchored in a gudgeon pin boss; a pair of elongated first bands, having the inner face thereof entirely open to said cavity each extending from a said connecting portion at least part-way round one of said thrust faces to form a bimetallic element therewith, each said first band being near the crown end of said skirt; a pair of elongated second bands, having the inner face thereof entirely open to said cavity each extending from a said connecting portion, being spaced apart from and substantially parallel with and independent from said first bands, each said second band extending at least part-way round one of said thrust faces to form a bimetallic element therewith, and each said second band being nearer to the open end of said skirt than each of said first band; and a pair of further portions each interconnecting one of said connecting portions, one of said first bands, and one of said second bands, with another of said connecting portions, first bands, and second bands, whereby said second bands, being nearer to the open end of said skirt, exert a greater degree of thermal expansion control for a given temperature change than do said first bands which are near the crown end of the skirt.
 2. A light metal piston as claimed in claim 1 wherein each said further portion extends around a said gudgeon pin bore, and Interconnects a pair of said connecting portions each anchored in opposite sides of the same gudgeon pin boss.
 3. A light metal piston as claimed in claim 2 wherein each expansion control insert is symmetrical about a longitudinal plane of the piston parallel to and adjacent to the plane containing the axis of the gudgeon pin bores.
 4. A light metal piston as claimed in claim 1 wherein each said further portion consists of an extension of one of said pairs of bands, interconnecting the ends of the bands of said pair, which ends are remote from said connecting portions, and said further portions passing right around the interior surface of the opposing thrust faces of the piston skirt.
 5. A light metal piston as claimed in claim 4 wherein each expansion control insert is symmetrical about a longitudinal plane of the piston substantially at right angles to the axis of the gudgeon pin bores.
 6. A light metal piston as claimed in claim 2 wherein said further portion extends below the gudgeon pin bore.
 7. A light metal piston as claimed in claim 2 wherein said further portion extends above the gudgeon pin bore. 